The present invention pertains to a valve arrangement for controlling the flow rate of a gas with a valve, with a crater or valve seat and with a valve closing arrangement for adjusting the gas flow rate
A prior-art valve arrangement is disclosed, e.g., in U.S. Pat. No. 5,265,594 with arrangements used especially in respirators. The arrangement generates different time-dependent respiration patterns for the patient. These are characterized by the gas flow as well as the respiration pressure at the patient, by means of the gas metering. The apparatuses are connected to a central gas supply for this purpose. The metering valve has the task of supplying the patient with a defined gas flow or to admit a defined overpressure to the patient. The needed mass flow rate or gas volume flow rate is set for this, in general, by changing the cross-sectional area of the gas line carrying the flow. The cross-sectional area of the gas line through which the gas flows is specially designed as a cylinder jacket surface, which is obtained from the circular valve cross section and the linear valve opening path located at right angles thereto. To set the cross-sectional area of the gas line through which the gas flows, an electrically actuated linear drive system is preferably used, whose force adjusts the valve opening path. The movement of the closing means of these prior-art electromechanical valve arrangements is damped very weakly due to the principle involved and it therefore tends to vibrate, especially when the valve arrangement is operated within a simple control circuit for the valve opening path, the gas flow or the patient pressure. Another prior-art arrangement is also shown in the Handbuch fxc3xcr das Intensivbeatmungsgerxc3xa4t Hamilton Veolar [Manual for the Hamilton Veolar Intensive Care Respirator], 1988 edition. A valve arrangement that meters a volume flow rate from a reservoir with variable pressure is described there. The arrangement is based in the control circuit for the gas flow rate on a displacement sensor, which measures the valve opening path. An attempt is made at increasing the stability of this control circuit by differentiating the signal of the valve opening path and superimposing it to the actuating signal of the drive system. The signal disturbances are amplified and the signal is, moreover, delayed in time due to the differentiation with this type of signal generation, so that the use of a signal obtained in this manner for damping has only limited effectiveness. One essential drawback of this prior-art valve arrangement is therefore that an acceptable build-up characteristic is given only up to a minimum valve adjustment time of a few millisec.
The object of the present invention is to provide an improved prior-art valve arrangement which makes it possible to markedly shorten the minimum valve adjustment time, to about half, at an equal build-up characteristic.
According to the invention, a valve arrangement for controlling the flow rate of a gas is provided with a valve with flow passage opening valve part, such as a crater or valve seat with a valve closing means for adjusting the gas flow rate. The arrangement includes an inflow line, a discharge line, a drive system for controlling the position of the valve closing means relative to the crater, a gas flow rate measuring transducer, and a velocity measuring transducer for measuring the velocity of the valve closing means relative to the crater providing an output signal. A control unit is provided for controlling the drive system by a control signal with the velocity measuring transducer output signal used to calculate the control signal for the drive system.
If the desired mass flow rate or gas volume flow rate, i.e., the gas flow rate, is to be set quickly and accurately, the movement of the closing means of the valve arrangement must be additionally damped from the outside, because a high degree of damping improves the possibility of adjusting the valve with little overshooting and rapidly. The damping is preferably accomplished according to the present invention by negatively sending the velocity of the closing means to the drive system. To achieve the necessary maximum effectiveness of damping, a velocity signal that is highly dynamic and especially has little disturbance and delay is used. The present invention correspondingly uses a means that obtains the velocity signal directly by measurement and ensures that this happens with only minimal time delays and disturbances. The valve adjustment time is markedly reduced as a result by about 50% while the design of the valve arrangement otherwise remains unchanged.
Due to the reduction of the valve adjustment time for the desired gas flow rate, it is also possible as a result to increase the rate of pressure rise at the patient.
It is also advantageous that due to the increased damping, the valve is able to cover an extended admission pressure range with approximately constant valve adjustment time for the gas flow rate.
The control signal for the drive system may be determined by forming the difference from a gas flow rate set point, the output signal of a velocity signal conditioner and the output signal of a gas flow rate signal conditioner. The control signal for the drive system may be determined by additionally forming the difference between the output signal of a current signal conditioner. The control signal for the drive system may be determined by forming the difference from the pressure set point, the output signal of the velocity signal conditioner and the output signal of the pressure signal conditioner. The control signal for the drive system may be determined by additionally forming the difference from the output signal of the current signal conditioner.
The control signal for the drive system may be determined by forming the difference from the pressure set point, the gas flow rate set point, the output signal of the velocity signal conditioner, the output signal of the gas flow rate signal conditioner, and the output signal of the pressure signal conditioner. The control signal for the drive system may be determined by additionally forming the difference from the output signal of the current signal conditioner.
The drive system designed may be for example an electrodynamic drive, an electromagnetic drive or a piezoelectric drive system.
The gas flow rate measuring transducer may be a thermal mass flow sensor. The gas flow rate measuring transducer may be a sensor based on a differential pressure measurement over a fixed pneumatic resistor.
The gas flow rate measuring transducer may be a sensor based on differential pressure measurement over an opening gap between the flow passage opening valve part e.g., the valve orifice and the valve closing means. The opening gap between the closing means and the valve part forming the orifice may be measured by means of a position sensor.
The velocity measuring transducer may be an electrodynamic sensor and may be placed preferably in the magnetic field of the drive system.
The ratio of the admission pressure before the valve and the back pressure behind the valve may advantageously be between 2 and 10. The ratio of the admission pressure before the valve and the back pressure behind the valve may advantageously be between 1 and 2.
The invention is particularly useful when used with respirators and anesthesia apparatuses for metering gas for respirated patients.
An exemplary embodiment of the present invention will be explained below on the basis of the figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.